JPS62141644A - Track servo circuit for optical disk - Google Patents

Abstract

PURPOSE:To decrease man-hour for testing and reduce cost by making automatic setting of optimum offset supplied to a track servo system possible. CONSTITUTION:Digital offset data given to a DA convertor is changed little by little from a - specified value to a + specified value applying focus and track servo, and output of an AD convertor 6 in the group section of a light disk is examined every time, and a point where the output becomes minimum is found. Adjustment of offset of track servo is completed when set to an offset value at which sum signal output becomes minimum. Above-mentioned operation can be made automatically by inputting digital offset data from a microprocessor, not shown in the figure, to the DA convertor 4 and controlling by a program of the microprocessor.

Description

[Detailed Description of the Invention] [Summary] An optical disk device includes a DA converter that converts digital offset data into an analog value and an AD converter that converts a sum signal output into a digital value, and sequentially changes within a predetermined range. Add the offset value to the track servo system,
The offset is adjusted by determining the lowest point of the sum signal output and setting the offset at this time, and can be easily automated by microprocessor control.

[Industrial Application Field] The present invention relates to offset adjustment of a track servo of an optical disc. -Equipped with two servo systems.

In this track servo system, the laser beam deviates to the left or right with respect to the track center due to mechanical or circuit imbalance.

This is called offset, and must be corrected at the time of shipping test or some other time.

The present invention relates to a method for automatically performing this offset adjustment.

[Prior Art] As shown in FIG. 5(a), an optical disc is usually provided with a spiral or concentric groove called a pre-group in order to guide the recording trunk, and the circumference is divided into several parts. Each sector is provided with a portion called a preformat, in which information such as track numbers and sector numbers is inscribed in advance in the form of intermittent grooves on the extension of the pregroup.

As shown in FIG. 5(b), the reflectance of the laser beam is low in the pre-grouped portion due to diffuse reflection, and is extremely high in the ungrouped portion due to total reflection.

Therefore, the reflected signal from the optical disc becomes a high frequency signal in the preformat section.

FIG. 6 is a block diagram of main parts of the optical disc device.

The light emitted from the laser is turned into a parallel beam by a collimation lens, passes through a polarizing beam splitter, is reflected by a mirror, and is focused onto the recording layer of the optical disk by an objective lens.

The reflected light from the optical disk passes through the objective lens again, is reflected by a mirror, is reflected downward by a polarizing beam splitter, and one is reflected by a half mirror, detected by a photodetector, and input into a high-frequency signal amplifier. , the other is transmitted downward and detected by a 4-split photodetector, and is input to a position error signal processing circuit.

The output of the position error signal processing circuit is input to the focus and trunk servo, and the output performs fine adjustment of the objective lens.

The voice coil motor servo controls the movement of the optical head to a desired trunk based on track selection data from the microprocessor.

In the 4-split photodetector, the photodetection surface is divided into 4 parts a, b, c, and d, and the detection outputs are divided into four parts a, b, and c.

d, (a+d)-(b+c) becomes the focus error signal, (a+b)-(c+d) becomes the track error signal, and (a+b+c+d) becomes the sum signal.

At the position where the track error signal determined above is minimized, the laser beam is not at the center of the track due to mechanical and circuit imbalances, but is shifted to the left or right with respect to the center of the track.

This is an offset, and in order to correct this, conventionally, at the time of shipping inspection, the sum signal of the 4-split photodetector was observed with an oscilloscope with the focus and track servos applied, and the preformat section and group section were The offset adjustment trimmer resistor was used to adjust the modulation depth ratio to the maximum.

[Problems to be Solved by the Invention] According to the conventional offset adjustment method as described above, the steps of trimmer resistance adjustment and paint lock are required at the time of shipping inspection, which obstructs test automation and makes testing difficult. This increased man-hours and made it difficult to reduce costs.

The present invention aims to provide a novel optical disc track servo circuit that solves these problems.

[Means for Solving the Problems] FIG. 1 shows a principle block diagram of a track servo circuit for an optical disk according to the present invention.

In FIG. 1, 1 is a 4-split photodetector, 2 is a differential amplifier for trunk error signals, and 3 is an adder for sum signals.

These are originally provided in the optical system of the optical disc device. It is something. The 4-split photodetector of 1 may be divided into 2 parts.

4 is a DA converter which converts the given digital offset data into an analog signal.

5 is an adder which adds the output of the track error signal differential amplifier 2 and the output of the DA converter 4;

6 is an AD converter, which converts the output of the sum signal adder 3 into A
D-convert.

With focus and trunk servo applied, DA
The digital offset data given to the converter 4 is changed little by little from one predetermined value to ten predetermined values, and the output of the AD converter 6 in the group section of the optical disk is checked each time, to find the point where the output is minimum.

If the offset value is set to the minimum sum signal output, the adjustment of the track servo offset is completed.

The above operations can be performed by inputting digital offset data from a microprocessor (not shown) to the DA converter 4, inputting the output of the AD converter 6 to the microprocessor, and controlling it by the microprocessor's program.
It can be done automatically.

[Function] With the above configuration, when the offset value to be added to the track servo system is gradually changed from - to + within a predetermined range, the laser beam (focused and (approximately 1 μmφ) in a group (usually approximately 0
．． As shown in Figure (b), the sum signal output is high in the ungrouped part between the groups and low in the group part. The lowest value occurs when it is at the center.

Since the inter-track spacing is usually about 1.6 μm, if the offset is too large, it will affect the adjacent group and the sum signal output will decrease.

In this way, automatic setting of the optimum offset becomes possible under program control of the microprocessor already included in the optical disc device.

[Example] The present invention will be explained in more detail below with reference to an example circuit diagram shown in FIG.

In FIG. 3, 1 is a 4-split photodetector, 2 is a differential amplifier for track error signals, and 3 is an adder for sum signals.

4 is a DA converter which converts digital offset data from the microprocessor into an analog signal.

Reference numeral 5 denotes an adder that adds the output of the track error signal differential amplifier 2 and the output of the DA converter 4.

6 is an AD converter which converts an analog signal into a digital value and inputs its output to the microprocessor.

Reference numeral 7 denotes a sample-and-hold circuit, which samples and holds the output of the sum signal adder 3 at the group level position (3) shown in FIG. 4 under the control of the microprocessor. Enter.

Focus and track servos are applied, and the following control is performed by a microprocessor program (not shown).

(2) Output an offset value to the DA converter 4 by changing it little by little from - to + within a predetermined range.

(2) Take in the output of the AD converter 6 for each offset value.

■Compare the values each time and detect the minimum value.

(2) Set the offset value at which the sum signal becomes the minimum in the DA converter 4;

[Effects of the Invention] As explained above, according to the present invention, it is possible to automatically set the optimum offset to be given to the track servo system, thereby reducing testing man-hours and reducing costs. is extremely large.

[Brief explanation of drawings]

Fig. 1 is a principle block diagram of the present invention, Fig. 2 is a diagram showing the relationship between offset amount and sum signal output, Fig. 3 is a circuit diagram of an embodiment of the present invention, Fig. 4 is a diagram showing sampling points, FIG. 5 is a diagram for explaining pre-groups and pre-formats, and FIG. 6 is a block diagram of the main parts of the optical disc device. In the drawings, 1 is a 4-split photodetector, 2 is a differential amplifier for track error signals, 3 is an adder for sum signals, 4 is a DA converter, 5 is an adder (means),
Reference numeral 6 indicates an AD converter, and reference numeral 7 indicates a sample and hold circuit. Figure 1: A diagram of the principle of the present invention. Figure 1: Relationship between the offset amount and sum signal. Figure 2: Figure 3: A diagram showing the sampling points. Figure 4 (phantom (b)): Diagram explaining the pre-group and pre-format.
5 Figure

Claims (1)

[Claims] In an optical disc device, an adder (3) that creates a sum signal of a four-split photodetector (1).
An AD converter (6) that converts the output of
and an adding means (5) for adding the output of the differential amplifier (2) for tracking error signals, and the digital offset data is changed within a predetermined range and given when the focus and track servos are applied. A track servo circuit for an optical disc, characterized in that the digital offset data is set at a position where the output of the AD converter (6) is minimized by repeating this process.